The present invention relates to a surface treatment for a piston ring for use in internal combustion engines.
Recently, as internal combustion engines tend to have higher performance, an extended life for such internal combustion engines is in strongly demand, while the functional components of the engine are burdened with ever increasing severe conditions. Piston rings are accordingly being exposed more often than before to severe environments such as high engine revolution, high temperature, and high bearing pressure, whereby higher durability is being required of such piston rings.
Furthermore, demand for higher engine performance and a smaller engine size exists, which causes various combinations of piston rings to be employed in diesel and gasoline engines; such combinations include a combination of three compression rings and two oil rings, a combination of three compression rings and one oil ring, a combination of two compression rings and one oil ring, and a combination of one compression ring and one oil ring, where compression rings and oil rings constitute respective aspects of piston rings. As a means to improve durability of piston rings, abrasion resistance treatments are being applied to the sliding surface of the piston rings, that include hard chrome plating and nitriding.
Abrasion resistance of piston rings with a conventional chrome-plated layer is insufficient for operating conditions; A nitriding treatment provides excellent abrasion resistance, where it is used as a surface treatment for the first compression ring (top ring) which is used under severe operating conditions, and tends to. Nitriding treatments employed in conventional piston rings are not sufficient from the view point of abrasion resistance, scuffing resistance, and aggressive-proofness (capability of treatment not being aggresive against the counterpart of the piston, i.e. adjacent cylinder wall material).
Therefore, an object of the present invention is to provide a piston ring for internal combustion engines that has excellent abrasion resistance and scuffing resistance, and is capable of decreasing its aggressiveness as much as possible (i.e. capable of having excellent aggressive-proofness).
In order to accomplish the object described above, a piston ring is provided, according to an embodiment of the present invention, such that the piston ring, implemented either as a compression ring or oil ring, has an ion-plating deposition layer formed over the external circumferential sliding surface thereof. The deposition layer is made of a mixture of a first chromium nitride of CrN type and a second chromium nitride of Cr2N type, the mixing ratios in the mixture being more than 45.0 and less than 98.0 weight percent for the first chromium nitride and the remaining weight percent portion for the second chromium nitride.
According to another embodiment of the present invention, a piston ring is provided such that the piston ring, implemented either as a compression ring or oil ring, has an ion-plating deposition layer formed over the external circumferential sliding surface thereof, wherein the deposition layer is made of a mixture of a first chromium nitride of CrN type, a second chromium nitride of Cr2N type, and metallic chromium. The mixing ratios in the mixture being more than 45.0 and less than 98.0 weight percent for the first chromium nitride, more than 0.5 and not more than 15.0 weight percent for the metallic chromium, and the remaining weight percent portion for the second chromium nitride.
According to a further embodiment of the present invention, the ion-plating deposition layer formed over the external circumferential sliding surface of the piston ring, made of the mixture described in the above embodiments, is formed to have porosity of more than 0.5 and not more than 20.0 percent.
Thus, according to the present invention, a piston ring for internal combustion engines, is obtained that advantageously has excel lent abrasion resistance, scuffing resistance, aggressive-proofness, and peeling-proofness, thereby enabling demands to be satisfied for internal combustion engines of higher performance.